The present invention regards some improvements in construction of cell-containers for accumulators, especialy for those meant for construction.
The above-mentioned improvements regard the construction-form of the accumulator's cell-container and of its lid and the way the cell-lid is welded to the cell-container itself.
It is well-known that the overall-dimensions of accumulator's cell-containers have been standardized according to international specifications. This doubtlessly positive and necessary fact forces the constructors of accumulators to adopt construction solutions which, while keeping overall-dimensions in parity, enable an increase of useful volume of the electrolyte's flooding capacity, thus obtaining an increased energetic-capacity of the accumulator itself.
Another problem of equal importance is to obtain perfect seal-tightness in welding the cell-lid to the cell-container. Furthermore, during the service-life, the cell-lid tends to crack due to the inevitable elongation of the positive pole caused by the well-known phenomenons of electrochemical nature; the connected problem is thus to obtain that both, the cell-lid and the cell-container, stand the above-mentioned elongation without damage.
Constructors of industrial accumulators faced these problems and solved them in different ways. Regarding the overall-dimensions of cell-containers, for example, the usual technique provides parallelopiped-formed cell-containers obtained by molding in polypropylene or similar thermoplastic-materials. The standard thickness usually obtainable by this proceeding is of approx. 3 mm.
To avoid exceeding the standard overall-dimensions, the cell-lid is joined to the cell-container by butt-welding, founding the contacting parts of the lid to the rim of the cell-container. However, as the above-mentioned welding generates a perimetric-bead, it is actually necessary to trim the same in order to be able to place one accumulator along the other without losing any space (like, for example, in batteries of accumulators for traction). This trimming-operation, aside from the cost of the operation in itself, can lead to uncovering of points lacking material caused by, for example, imprisoned air-locks or, anyway, by bad welding; consequently, there exists a possibility of electrolyte-leaks or, still of the impossibility of automatically topping-up through the pneumatic top-cover.
The improvements object of the present invention solve all the problems related to the trimming of the bead, as the bead forms itself on the inside and not on the outside of the cell-container. This was made possible by two factors and precisely by (1) the particular conformation of the cell-lid and of the cell-container's rim provided with a male-female mating remaining with the standard overall-dimensions and (2) by the extremely reduced thickness of the cell-container's walls and that of the cell-lid's rim, reduced to more than a half in comparison to the generally used ones.
It is obvious that, if there were no reduction of thickness, the said solution of the cell-lid having an external rim in respect to the walls of the cell-container, would lead to an increase of the overall-dimensions of the battery. Furthermore, the construction-method of the cell-container itself should be kept present, as it is generally made by injection-molding, usually in polypropylene, whereby in the present invention it is obtained by blow-forming. This process of blowing the form of the cell-container permits to obtain extremely reduced thickness of its walls, arriving up to 60% in comparison to the thermoplastic-molding process; it enables forms with undercuts otherwise not obtainable or prohibitedly expensive, due to the extremely complex molds needed in such a case.
The above-mentioned blow-forming process permits the reduction of thickness of the cell-container's walls, as well as considerable savings of material. Another advantage is represented by the fact that the molds involved are very simple and made in easily-workable materials.
Another element of basic importance deriving from the present invention is that it is possible to increase the welding-surface between the cell-lid and the cell-container, independently from the thickness. This is due to the special forming of the head of the terminal part of the cell-container obtained directly by the form of the blowing-mold. Not the least advantage of the present invention is, further, to have foreseen perimetric-horizontal recessings, obtained directly in forming and placed at various standardized levels so that by one and only blowing it becomes possible to obtain cell-containers with modular-systems, of various heights, depending on necessity. In this case the advantage for the constructor lies in the possibility to reduce the number of forming-molds, obtaining from one mold several cell-containers of different height and capacity; the constructor of industrial-batteries, on his part, can reduce his store, still having the possibility to assemble batteries of different capacities. Another function of said horizontal recessings is to avoid possible deformations of the cell-container, either in its terminal part where it is matched and welded to the cell-lid or in its central part, particularly in case of considerably high cell-containers. Said recessings have still another, not secondary, function of guiding and locking the iner cells of the battery.
The last improvement, part of the present invention, regards the cell-lid of the accumulator, made in such a way to stand, without damage, the elongation of the poles. The known technique in this field regards performances using a plastic-type binder fitted-in between the cell-lid and the cell-container, this type permitting a certain elongation of the poles. Said solution is mostly used in accumulators for cars, but it doesn't solve the problem for industrial accumulators, especially those meant for traction, where the height of the cells may arrive to 650 mm and where the said elongations are consequently increased. Another known solution consists in having created, within the cell-lid and in the area around each of the poles a series of concentric-rings which, due to their form and construction, permit some elongation of the poles.
The improvement regarding the cell-lid in the present invention solves the problem of deformation of the same and, thus, of its ability to stand the elongation of the poles, as said cell-lid is constructed in a special, externally concave form. By this extremely simple solution, which is at the same time extremely functional and economical, the elastic-tensions developed by the elongation of the poles are evenly distributed on the whole of the cell-lid's surface instead of being concentrated on a reduced area as it is generally the case. In this way the possibility of the cell-lid's cracking under the pressure of the differently distributed tensions is nullified or, in any case, drastically reduced. Another interesting characteristics of not secondary importance presented by this solution is that, due to its special convex-form, the cell-lid holds possible leaks of electrolyte caused by overflowing of the central top-cover when recharging distilled water. Thus the process of removal and cleaning-up of the overflown liquid, in case such a thing happens, is simplified and the chance that the liquid might run-down between the accumulators and settle at the bottom of the accumulator's box which, although usually constructed in plastified-iron, could be, at least in some weak-points, effected by the action of electrolyte, is avoided.
Another characteristics of the present improvement is that the cell-lid is furnished with a ring molded around the inlet of the electrolyte, thus avoiding eventual leaks when recharging the battery while the top-cover is removed. In this way the application of a gasket on the top-cover becomes unnecessary, as said barrier, circular and deformable, acts as a sealing-element.